In gas gathering and transportation systems, fluid in pipelines has been a constant source of problems and expense. In depleted fields in particular, where wells must be pulled down to a few pounds or a vacuum to maintain production, the problem is worse. For many years the amount of vacuum was limited due to the use of compressors which leak oxygen past mechanical seals and rings. The advent of liquid ring and rotary liquid screw type compressors supplied the industry with the ability to increase production in the Panhandle West gas fields, and many other fields, by reducing the pressure below atmospheric without introducing oxygen into the system. Over the past 20 years this has led to entire fields involving thousands of wells which must be kept at various vacuums, with many at 22″, which is close to the maximum that can be reached at the elevation of the Panhandle West fields.
A method to extract fluid out of these lines has remained many years behind the technology used to place them in the existing situation. As the secondary recovery technique progressed, the time increased for wells and gathering lines to pressure up and blow the fluid out of the drips when the compressors were shut down or bypassed. (A “drip” is typically an underground vessel designed to catch and hold fluids which drop out of natural gas during transportation through pipelines). Over the past several years the situation has evolved into a major problem. Drip trucks cannot pull fluid out unless the system is vented or left down for long periods of time in order to lower the amount of vacuum. In many cases entire sections of a field involving several wells must be shut down and lines allowed to suck in air. After a point is reached where a truck can empty the drip, the wells are opened and lines purged to atmosphere to evacuate the oxygen which was sucked in.
The wasted power for compressors, the amount of gas lost with air during the purging process, and the hours of trucking cost and down time are unacceptable. The danger of environmental impact problems due to the wasted natural gas is increasing because the oxygen tends to lay in the low parts of the lines and a large amount of gas must be vented to attain the 50 ppm or less oxygen content required to enter the pipeline system and resume normal production delivery. Many of these wells will not return to positive pressure in several months or years. Even in newer wells, gas is wasted and the environment is impacted as thousands of mcf are lost daily to the atmosphere when vacuum trucks or gear type pumps are used to load the drip trucks.
One of the insurmountable problems with all prior art is the mixture of the fluid in these drips. The fluid is a high gravity condensate mixed in various degrees of percentage with water. Pumps used to move normal liquefied petroleum gas or Y-Grade products are damaged or unsuitable for moving water and heavier liquids. Pumps used to move fluids are not capable of moving the Y-Grade type hydrocarbons. Vacuum type pumps are limited to the same or less vacuum capability as the elevation of the gathering system.